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T-Mobile USA is committed to a partnership with Public Safety to provide Phase I and Phase II Enhanced 9-1-1 service for our subscribers and roaming customers in times of emergency. What is Basic 9-1-1 service? Basic 9-1-1 service is an emergency telephone system which automatically connects wireless 9-1-1 calls to a designated 9-1-1 Communications Center. Basic 9-1-1 may or may not provide the wireless phone's 10-digit call-back number and estimated location. The handset must have battery power and be in a coverage area to complete a 9-1-1 call. What is Enhanced 9-1-1 Phase I service? Enhanced 9-1-1 Phase I service is the first step in providing better emergency response service to wireless 9-1-1 callers. Public Safety/9-1-1 Communications Centers need to send a letter to T-Mobile requesting Phase I service deployment at their agency. Once Phase I service has been implemented, when a wireless 9-1-1 call comes into the 9-1-1 Communications Center (also called a Public Safety Answering Point or PSAP), the call-taker's computer screen will show the wireless phone's 10-digit call-back number if one has been assigned to the calling handset. In the event the wireless phone call is dropped, the call-taker may contact the caller. Phase I service also identifies the cell site/sector location information that the call was made on to the call-taker's computer screen. This provides the call-taker with a general location (i.e. within the site coverage area) of the caller. What is Enhanced 9-1-1 Phase II service? Public Safety/9-1-1 Communications Centers need to send a letter to T-Mobile requesting Phase II service deployment at their agency. With Phase II service, the location information that is provided to the 9-1-1 Communications Center is the approximate X, Y (longitude, latitude) location of the handset making the call. This location information is typically more accurate than the Phase I location information (cell site/sector). As with Phase I, Phase II service allows call takers to receive both the caller's wireless phone number and their location information. Since early 2004, T-Mobile has been deploying a network-based Phase II solution. T-Mobile's solution-referred to as U-TDOA, Uplink-Time Difference of Arrival-does not require customers to purchase a new handset.